The present invention relates to the field of energy distribution. More particularly, the present invention pertains to the structure of a vacuum switching tube in which switching contacts are directly surrounded by an insulating housing.
Vacuum switches are used to interrupt current in energy distribution networks. They are also used in power supplies for large power consumption devices. Vacuum switches essentially include a vacuum switching tube and a drive device. The vacuum switching tube is the actual switching element, and it has an axially movable contact piece that is rigidly coupled with the drive device. The drive device is designed such that a certain distance between contacts exists when the switch is closed. This distance is denoted the contact stroke.
German Patent No. DE 19 15 198 discloses a vacuum switching tube that has a housing which includes a metallic hollow cylinder in the region of the contact pieces. The metallic hollow cylinder directly surrounds the contact pieces. Hollow cylinder insulators, generally made of ceramic material, are soldered on at both ends.
In addition to the aforementioned vacuum switching tubes, it is also common to provide a cylindrical housing in the vacuum switching tube which comprises one or two axially adjacent insulators as disclosed in German Patent Nos. DE 25 35 150, DE 26 12 129, DE 27 25 092. In these switches, a hollow cylindrical metal shield is provided to protect an inner wall of the insulator against the condensation of metal vapor. This metal shield surrounds the contact pieces directly, at a distance, and is attached to either the insulator, at the seam of the two insulators, or to one of the two end plates of the housing.
A vacuum switching tube disclosed in U.S. Pat. No. 5,004,877 has a hollow cylinder insulator as an axially extending housing part and no metal shield is provided between the contact pieces and the insulator. A metal shield is attached to the fixed contact pin at one end of the insulator to prevent the condensation of metal vapor.